Re: [PATCH Kernel v20 6/8] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap

Kirti Wankhede
2020-05-15T04:16:58Z

On 5/15/2020 8:57 AM, Alex Williamson wrote:
> On Fri, 15 May 2020 02:07:45 +0530
> Kirti Wankhede <kwankhede@nvidia.com> wrote:
>
>> DMA mapped pages, including those pinned by mdev vendor drivers, might
>> get unpinned and unmapped while migration is active and device is still
>> running. For example, in pre-copy phase while guest driver could access
>> those pages, host device or vendor driver can dirty these mapped pages.
>> Such pages should be marked dirty so as to maintain memory consistency
>> for a user making use of dirty page tracking.
>>
>> To get bitmap during unmap, user should allocate memory for bitmap, set
>> it all zeros, set size of allocated memory, set page size to be
>> considered for bitmap and set flag VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP.
>>
>> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
>> Reviewed-by: Neo Jia <cjia@nvidia.com>
>> ---
>> drivers/vfio/vfio_iommu_type1.c | 77 ++++++++++++++++++++++++++++++++++-------
>> include/uapi/linux/vfio.h | 10 ++++++
>> 2 files changed, 75 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index b76d3b14abfd..a1dc57bcece5 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -195,11 +195,15 @@ static void vfio_unlink_dma(struct vfio_iommu *iommu, struct vfio_dma *old)
>> static int vfio_dma_bitmap_alloc(struct vfio_dma *dma, size_t pgsize)
>> {
>> uint64_t npages = dma->size / pgsize;
>> + size_t bitmap_size;
>>
>> if (npages > DIRTY_BITMAP_PAGES_MAX)
>> return -EINVAL;
>>
>> - dma->bitmap = kvzalloc(DIRTY_BITMAP_BYTES(npages), GFP_KERNEL);
>> + /* Allocate extra 64 bits which are used for bitmap manipulation */
>> + bitmap_size = DIRTY_BITMAP_BYTES(npages) + sizeof(u64);
>> +
>> + dma->bitmap = kvzalloc(bitmap_size, GFP_KERNEL);
>> if (!dma->bitmap)
>> return -ENOMEM;
>>
>> @@ -999,23 +1003,25 @@ static int verify_bitmap_size(uint64_t npages, uint64_t bitmap_size)
>> }
>>
>> static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>> - struct vfio_iommu_type1_dma_unmap *unmap)
>> + struct vfio_iommu_type1_dma_unmap *unmap,
>> + struct vfio_bitmap *bitmap)
>> {
>> - uint64_t mask;
>> struct vfio_dma *dma, *dma_last = NULL;
>> - size_t unmapped = 0;
>> + size_t unmapped = 0, pgsize;
>> int ret = 0, retries = 0;
>> + unsigned long pgshift;
>>
>> mutex_lock(&iommu->lock);
>>
>> - mask = ((uint64_t)1 << __ffs(iommu->pgsize_bitmap)) - 1;
>> + pgshift = __ffs(iommu->pgsize_bitmap);
>> + pgsize = (size_t)1 << pgshift;
>>
>> - if (unmap->iova & mask) {
>> + if (unmap->iova & (pgsize - 1)) {
>> ret = -EINVAL;
>> goto unlock;
>> }
>>
>> - if (!unmap->size || unmap->size & mask) {
>> + if (!unmap->size || unmap->size & (pgsize - 1)) {
>> ret = -EINVAL;
>> goto unlock;
>> }
>> @@ -1026,9 +1032,15 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>> goto unlock;
>> }
>>
>> - WARN_ON(mask & PAGE_MASK);
>> -again:
>> + /* When dirty tracking is enabled, allow only min supported pgsize */
>> + if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&
>> + (!iommu->dirty_page_tracking || (bitmap->pgsize != pgsize))) {
>> + ret = -EINVAL;
>> + goto unlock;
>> + }
>>
>> + WARN_ON((pgsize - 1) & PAGE_MASK);
>> +again:
>> /*
>> * vfio-iommu-type1 (v1) - User mappings were coalesced together to
>> * avoid tracking individual mappings. This means that the granularity
>> @@ -1066,6 +1078,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>> ret = -EINVAL;
>> goto unlock;
>> }
>> +
>> dma = vfio_find_dma(iommu, unmap->iova + unmap->size - 1, 0);
>> if (dma && dma->iova + dma->size != unmap->iova + unmap->size) {
>> ret = -EINVAL;
>> @@ -1083,6 +1096,23 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>> if (dma->task->mm != current->mm)
>> break;
>>
>> + if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&
>> + (dma_last != dma)) {
>> +
>> + /*
>> + * mark all pages dirty if all pages are pinned and
>> + * mapped
>> + */
>> + if (dma->iommu_mapped)
>> + bitmap_set(dma->bitmap, 0,
>> + dma->size >> pgshift);
>
> Nit, all the callers of update_user_bitmap() precede the call with this
> identical operation, we should probably push it into the function to do
> it.
>
>> +
>> + ret = update_user_bitmap(bitmap->data, dma,
>> + unmap->iova, pgsize);
>> + if (ret)
>> + break;
>> + }
>> +
>
> As noted last time, the above is just busy work if pfn_list is not
> already empty. The entire code block above should be moved to after
> the block below. Thanks,
>

pfn_list will be empty for IOMMU backed devices where all pages are
pinned and mapped, but those should be reported as dirty. So moved it
back above empty pfn_list check.

Thanks,
Kirti

> Alex
>
>> if (!RB_EMPTY_ROOT(&dma->pfn_list)) {
>> struct vfio_iommu_type1_dma_unmap nb_unmap;
>>
>> @@ -2447,17 +2477,40 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>>
>> } else if (cmd == VFIO_IOMMU_UNMAP_DMA) {
>> struct vfio_iommu_type1_dma_unmap unmap;
>> - long ret;
>> + struct vfio_bitmap bitmap = { 0 };
>> + int ret;
>>
>> minsz = offsetofend(struct vfio_iommu_type1_dma_unmap, size);
>>
>> if (copy_from_user(&unmap, (void __user *)arg, minsz))
>> return -EFAULT;
>>
>> - if (unmap.argsz < minsz || unmap.flags)
>> + if (unmap.argsz < minsz ||
>> + unmap.flags & ~VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP)
>> return -EINVAL;
>>
>> - ret = vfio_dma_do_unmap(iommu, &unmap);
>> + if (unmap.flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) {
>> + unsigned long pgshift;
>> +
>> + if (unmap.argsz < (minsz + sizeof(bitmap)))
>> + return -EINVAL;
>> +
>> + if (copy_from_user(&bitmap,
>> + (void __user *)(arg + minsz),
>> + sizeof(bitmap)))
>> + return -EFAULT;
>> +
>> + if (!access_ok((void __user *)bitmap.data, bitmap.size))
>> + return -EINVAL;
>> +
>> + pgshift = __ffs(bitmap.pgsize);
>> + ret = verify_bitmap_size(unmap.size >> pgshift,
>> + bitmap.size);
>> + if (ret)
>> + return ret;
>> + }
>> +
>> + ret = vfio_dma_do_unmap(iommu, &unmap, &bitmap);
>> if (ret)
>> return ret;
>>
>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>> index 123de3bc2dce..0a0c7315ddd6 100644
>> --- a/include/uapi/linux/vfio.h
>> +++ b/include/uapi/linux/vfio.h
>> @@ -1048,12 +1048,22 @@ struct vfio_bitmap {
>> * field. No guarantee is made to the user that arbitrary unmaps of iova
>> * or size different from those used in the original mapping call will
>> * succeed.
>> + * VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP should be set to get dirty bitmap
>> + * before unmapping IO virtual addresses. When this flag is set, user must
>> + * provide data[] as structure vfio_bitmap. User must allocate memory to get
>> + * bitmap, zero the bitmap memory and must set size of allocated memory in
>> + * vfio_bitmap.size field. A bit in bitmap represents one page of user provided
>> + * page size in 'pgsize', consecutively starting from iova offset. Bit set
>> + * indicates page at that offset from iova is dirty. Bitmap of pages in the
>> + * range of unmapped size is returned in vfio_bitmap.data
>> */
>> struct vfio_iommu_type1_dma_unmap {
>> __u32 argsz;
>> __u32 flags;
>> +#define VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP (1 << 0)
>> __u64 iova; /* IO virtual address */
>> __u64 size; /* Size of mapping (bytes) */
>> + __u8 data[];
>> };
>>
>> #define VFIO_IOMMU_UNMAP_DMA _IO(VFIO_TYPE, VFIO_BASE + 14)
>